The variability of pressures resulting from plunging wave impact on a smooth vertical cylinder is examined. Based on laboratory measurements the fluctuations in the pressure characteristics are found to be associated with two main factors; one is the significant shift in the wave breaking location relative to the cylinder location and the other is the randomness of the wave breaking kinematics and the trapped air dynamics. The variation of the peak pressure magnitudes associated with the latter is presented. Both the mean characteristics and the probability distributions are examined.


In the design of offshore structures one is often seeking an estimate of the extreme wave loads. It is long known that such a loading can result from waves breaking onto the structure. Research in recent years (e.g. Sawaragi and Nocmno 1984, Kjeldsen et.al. 1986. Chan and Melville 1987, 1988, Basco and Niedzwecki 1989, and Tan et.al. 1989) have in fact shown that wave impact forces can be more than two times higher than non-impact forces from waves of comparable amplitudes. Moreover, the corresponding impact pressures can be more than ten times higher compared to non-impact pressures. These impact loads are highly impulsive and transient in nature and the physics of the impact process is complex. In a hostile ocean environment, particularly during store weather the chances of encountering such wave impacts are very high. Consequently, a good knowledge of the mechanics and dynamics of wave impact is essential especially when the overall objective is to produce a safe and economical structure. Also, plunging wave impact occurs not at one critical structure location relative to the wave breaking location, but over a range of locations within the region of wave breaking Chan and Melville 1987,1988, Tan et.al. (1989).

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